This invention relates to a protective circuit for a supersonic humidifier, particularly to one utilizing a compare circuit to obtain working voltage at two terminals of an ultrasonic vibrating member for deciding to turn off or continue to let a switch on so that the humidifier may be timely stopped in case of no water left in a water tank, without possibility of burning up.
Nowadays, conventional supersonic humidifiers all use a detective element in a water tank to detect if there is water in the water tank or not so that an ultrasonic vibrating member should continue to operate or not with the power switch being on. In this way the humidifier may operate normally, protected from burning up in case of no water in the water tank.
However, the detective element such as a vibrating needle, a magnetic switch, a HALL IC in cooperation of a float occupies large dimensions, hardly applicable to a comparatively small humidifier. Besides, in case that water in the water tank is used up, or the float is placed upside down, the detecting element may detect erroneously to let the humidifier continue to operate, resulting in burning up.